The present invention relates to the field of image processing, and more particularly to a dynamic thresholding method for converting an ultrasonic C-scan image into a binary flaw-no flaw image.
Ultrasonic pulse-echo inspection of titanium and other large grain metal objects is plagued by grain noise produced by ultrasonic reflections from large grain interfaces. Grain noise occurs because the microstructure of metals such as titanium or the like can be coarse which causes the grains of the microstructure to return signals during a raster scan of the object with an ultrasonic transducer. Due to the extruding and forging processes used in forming titanium parts, grain structure, and therefore grain noise, can vary significantly between different regions of an object. Grain noise can typically vary between 6-20 dB. Grain noise can mask or conceal flaw indications in a defective region or produce false indications of flaws in defect free regions. False flaw indications can result in a defect free object being rejected for use in a particular application. Masked flaw indications can result in the unintentional use of a flawed part. Obviously, either masked flaw indications or false flaw indications can result in significant waste of time and materials in the manufacture of metal-parts and/or an undesirable increased risk of part failure.